1. Field of the Invention
The present invention relates to a high frequency receiving device used for a TV receiving tuner or the like, and an integrated circuit used for the same.
2. Description of the Related Art
A conventional high frequency receiving device will be described in the following with reference to the drawings. FIG. 8 is a block diagram of a conventional high frequency receiving device.
In FIG. 8, a high frequency signal ranging from 55.25 MHz to 801.25 MHz is inputted to input terminal 1. The high frequency signal is fed to single tuning filter 2 that is a single tuning type filter. The single tuning filter 2 includes one variable capacity diode and is able to vary the tuning frequency by using a tuning voltage applied to frequency variable terminal 2a. The tuning frequency of single tuning filter 2 is within the range of UHF broadcast band (367.25 MHz to 801.25 MHz).
The output of single tuning filter 2 is connected to high frequency amplifier 3, and high frequency amplifier 3 amplifies UHF broadcast band signals. The output of high frequency amplifier 3 is connected to double tuning filter 4. The double tuning filter 4 includes two variable capacity diodes and is able to vary the tuning frequency by using a tuning voltage applied to frequency variable terminal 4a. 
The output signal of double tuning filter 4 is inputted to one side of mixer 5, and a local oscillation signal produced by dividing the local oscillation output signal of local oscillator 6 by means of frequency divider 7 is inputted to the other side thereof. The mixer 5 mixes UHF broadcast band signal having passed through double tuning filter 4 with the local oscillation signal, and converts it to intermediate frequency signal 45.75 MHz. The output of mixer 5 is connected to intermediate frequency filter 8, and unnecessary signal is attenuated by occupied frequency band 6 MHz. The output signal of intermediate frequency filter 8 is supplied to output terminal 9 via the intermediate frequency amplifier.
And these single tuning filter 2, high frequency amplifier 3, double tuning filter 4, mixer 5 and intermediate frequency filter 8 configure UHF signal receiver 10.
Also, VHF band signal is supplied to input terminal 1. VHF signal receiver 11 receives VHF broadcast band signals ranging from 55.25 MHz to 361.25 MHz. The VHF signal receiver 11 comprises single tuning filter 12, high frequency amplifier 13, double tuning filter 14, and mixer 15.
First, single tuning filter 12 includes one variable capacity diode, and is able to vary the tuning signal by using the tuning voltage applied to frequency variable terminal 12a. The output of single tuning filter 12 is connected to high frequency amplifier 13, and high frequency amplifier 13 amplifies the VHF broadcast band signals.
The output of high frequency amplifier 13 is connected to double tuning filter 14. The double tuning filter 14 includes two variable capacity diodes, and is able to vary the tuning frequency by using the tuning voltage applied to frequency variable terminal 14a. The output signal of double tuning filter 14 is inputted to one side of mixer 15, and local oscillation signal produced by dividing the local oscillation output signal of local oscillator 6 by means of frequency divider 16 is inputted to the other side thereof. The mixer 15 mixes VHF broadcast band signal having passed through double tuning filter 14 with the local oscillation signal, and converts it to intermediate frequency signal 45.75 MHz. And, the output of mixer 15 is connected to the input of intermediate frequency filter 8.
Next, at local oscillator 6, oscillator 17 produces local oscillation output signals. Tuner 18 is connected to input 17a and 17b of oscillator 17. The tuner 18 comprises series connection body 21 with variable capacity diode 19 and capacitor 20, and inductor 22 parallel-connected to series connection body 21.
PLL circuit 23 is a PLL circuit which produces control voltage for frequency control, and the output of oscillator 17 is connected to the input of PLL circuit 23. And, the tuning voltage, control voltage outputted from output terminal 23a of PLL circuit 23, is supplied to variable capacity diode 19 of tuner 18, and variable capacity diodes of single tuning filter 2, double tuning filter 4, single tuning filter 12, and double tuning filter 14.
Next, the operation of local oscillator 6 and frequency divider 7, 16 in a conventional high frequency receiving device will be described with reference to FIG. 9. FIG. 9 is a characteristic diagram of a local oscillator, and horizontal axis 31 stands for local oscillation frequency (MHz) applied to mixer 5 or 15, and vertical axis 32 is tuning voltage (V) outputted from PLL circuit 23.
In FIG. 9, curve 33 shows the characteristic of local oscillation signal supplied to mixer 5 of UHF signal receiver 10. It is configured in that oscillation signals of about 350 MHz and about 850 MHz can be obtained respectively when the tuning voltage of PLL circuit 23 is 1V and 24V in UHF broadcast signal receiving mode.
Curve 34 shows the characteristic of local oscillation signal supplied to mixer 15 during reception of VHF high-band broadcast band signals in a conventional high frequency receiving device which divides the output frequency of local oscillator 6 by frequency divider 16 as it is. Also, curve 35 shows the characteristic of local oscillation signal suited for receiving VHF high-band broadcast band signals.
Curve 36 shows the characteristic of local oscillation signal supplied to mixer 15 during reception of VHF low-band broadcast band signals in a conventional high frequency receiving device which divides the output frequency of local oscillator 6 by frequency divider 16 as it is. Also, curve 37 shows the characteristic of local oscillation signal suited for receiving VHF low-band broadcast band signals.
As prior art document information related to this invention, for example, Japanese Laid-open Patent 2000-295539, Japanese Laid-open Patent 2002-118795, or Japanese Laid-open Patent H1-265688 is well-known.
However, in such a conventional high frequency receiving device, there arises a subject such that within the tuning voltage variable range there is a frequency range that cannot be oscillated, and a certain frequency range cannot be received. That is, as shown in FIG. 9, when receiving VHF high-band broadcast band signals, the local oscillation signal characteristic has to be originally as shown by curve 35. However, in case a local oscillation output signal shown by curve 33 is divided by frequency divider 16 as it is, the characteristic of frequency dividing signal supplied to mixer 15 or the local oscillation signal will be as shown by curve 34, and within the variable range of tuning voltage, there exists a frequency range that cannot be oscillated with respect to the frequency range essentially needed.